The present invention relates to a semiconductor module, and more particularly, a semiconductor module comprising a plurality of semiconductor elements connected in parallel to each other.
FIG. 7A is a plan view of a conventional semiconductor module (a lid portion is not shown), and FIG. 7B is a cross sectional view along lines IVxe2x80x94IV in FIG. 7B.
As shown in FIGS. 7A and 7B, in the conventional semiconductor module generally denoted at 200, an insulation substrate 71 is placed on a base plate 1. In a front surface of the insulation substrate 71, a gate wire pattern 14, a collector wire pattern 72, and an emitter wire pattern 73 are formed. On the collector wire pattern 72, a plurality of insulated gate bipolar transistors 31 (hereinafter referred to as xe2x80x9cIGBTsxe2x80x9d) and free wheel diodes 32 (hereinafter referred to as xe2x80x9cdiodesxe2x80x9d) are disposed. Collectors of the IGBTs 31 and cathodes of the diodes 32 are connected with the collector wire pattern 72.
As shown in FIG. 7A, the emitter wire pattern 73 is formed in the shape of the letter xe2x80x9cLxe2x80x9d along two sides of the collector wire pattern 72. Meanwhile, the gate wire pattern 14 is formed along other one side of the collector wire pattern 72. This is for the ease of work at a bonding step for connecting the respective wire patterns with the IGBTs 31 and the like.
A back surface pattern 74 is formed in a back surface of the insulation substrate 71, and fixed on the base plate 1 by a solder layer 2.
The IGBTs 31 and the diodes 32 are connected respectively with the gate wire pattern 14 and the emitter wire pattern 73 by bonding wires 35 and 34. Further, the gate wire pattern 14, the emitter wire pattern 73 and the collector wire pattern 72 are connected respectively with gate electrodes 41, collector electrodes 42 and emitter electrodes 43 by bonding wires 36, 37 and 38.
A case portion 6 is formed on the base plate 1 so as to surround the insulation substrate 71. After wire bonding of the IGBTs 31 and the like, a gel material 7 for sealing is injected inside the case portion 6, and a lid portion 8 is put on.
In the semiconductor module 200 with the conventional structure, since wiring distances from the emitter electrodes 43 to the diodes 32 arranged in parallel to each other are different from each other, loads (such as impedance, capacitance) of the wires are different from each other among the diodes 32. Hence, even when the semiconductor module is applied with a constant voltage, for example, voltages applied to the diodes 32 arranged in parallel to each other are different from each other, which may destroy some of the diodes. This also applies to the IGBTs 31.
In addition, to allow the semiconductor module to carry a large current, it is necessary that a cross section of the wire patterns has a large size. In contradiction to this, if the wire patterns are thick, there is a problem that the insulation substrate 71 cracks due to a difference in expansion coefficient between the insulation substrate 71 of a ceramic material and the wire pattern 73 of metal. Further, if the width of the wire pattern 73 is large, there is a problem that it is difficult to complete the semiconductor module in a small size.
In view of this, a first object of the present invention is to provide a semiconductor module in which wiring lengths of semiconductor elements arranged in parallel to each other are approximately the same.
A second object of the present invention is to provide a semiconductor module in which a cross section of wire patterns has a large size without increasing a module size.
The present invention is directed to a semiconductor module in which at least two semiconductor elements arranged along a certain direction, and at least two electrode pad regions arranged along a direction approximately perpendicular to said certain direction, are respectively connected in parallel to each other, characterized in comprising:
a) a base plate;
b) a lower layer substrate comprising: a first insulation substrate in approximately rectangular shape with the back surface fixed on said base plate; a first and a second electrode pads in approximately identical shapes disposed on a front surface of said first insulation substrate along one side of said first insulation substrate so as to be juxtaposed to each other in this order from a corner portion of said one side; and first and second wires which are juxtaposed to each other along other side of said first insulation substrate approximately perpendicular to said one side and including said corner portion of said one side, said second wire extending by the side of said first and said second electrode pads, and said first wire extending by the side of said first electrode pad with said second wire interposed;
c) an upper layer substrate disposed on said lower layer substrate, comprising: a second insulation substrate in approximately rectangular shape; and a first bridge wire connecting said first wire with said first electrode pad and a second bridge wire connecting said second wire with said second electrode pad, which are formed in a back surface of said second insulation substrate;
d) a first semiconductor element electrically connected with said first wire and a second semiconductor element electrically connected with said second wire, which are formed in a front surface of said second insulation substrate; and
e) a cap disposed on said base plate so as to cover said lower layer substrate, said upper layer substrate, and said first and said second semiconductor elements.
In this semiconductor module, wiring lengths from the semiconductor elements to emitter electrodes are approximately uniform between the semiconductor elements arranged in parallel to each other.
This allows achieving approximately the same loads, such as impedances, between the wires arranged in parallel to each other.
As a result, it is possible to prevent overload-induced malfunction of some semiconductor elements occurring in a conventional semiconductor module, and hence, to improve the reliability of the semiconductor module.
Since a semiconductor module herein described comprises two semiconductor elements, a semiconductor module comprising three or more semiconductor elements is also within the scope of the present invention. Further, the cap portion is formed by a case portion and a lid portion.
The present invention is also directed to a semiconductor module further comprising a solder resist layer coating a front surface of said lower layer substrate, characterized in that said first bridge wire and both of said first wire and said first electrode pad are connected with each other by solder layers buried in holes formed in said solder resist layer, while said second bridge wire and both of said second wire and said second electrode pad are connected with each other by solder layers buried in holes formed in said solder resist layer.
Use of the solder resist layer makes it easy to use a structure in which wire layers intersect each other.
A surface area of said lower layer substrate is preferably larger than a surface area of said upper layer substrate, and said first and said second wires and said first and said second electrode pads extend preferably beyond said upper layer substrate covering said lower layer substrate.
With this structure, it is easy to perform wire bonding.
The first and said second semiconductor elements and said first and said second wires may be connected with each other by bonding wires and said first and said second electrode pads and an external electrode may be connected with each other by bonding wires.
The present invention is directed further to a semiconductor module in which at least two semiconductor elements juxtaposed to each other along a certain direction, and an electrode pad region arranged along a direction approximately perpendicular to said certain direction, are connected with each other, characterized in comprising:
a) a base plate;
b) a lower layer substrate comprising: a first insulation substrate in approximately rectangular shape with the back surface fixed on said base plate; and a lower layer wiring conductor in approximately rectangular shape formed in a front surface of said first insulation substrate, wherein said lower layer wiring conductor has a slit cut toward inside from one of the corner portions or the near, an area of said lower layer wiring conductor along one side adjacent to said corner portion is a connection area with said semiconductor elements, and an area of said lower layer wiring conductor along other side adjacent to said corner portion is said electrode pad region;
c) an upper layer substrate disposed on said lower layer substrate, comprising: a second insulation substrate in approximately rectangular shape; and an upper layer wiring conductor in approximately rectangular shape formed in a back surface of said second insulation substrate and connected with said lower layer wiring conductor via a solder layer, wherein said upper layer wiring conductor has a slit in a portion overlapping said slit of said lower layer wiring conductor in the approximately identical shape;
d) a first and a second semiconductor elements electrically connected with said connection area of said lower layer wiring conductor, which are formed in a front surface of said second insulation substrate; and
e) a cap disposed on said base plate so as to cover said lower layer substrate, said upper layer substrate, and said first and said second semiconductor elements.
In this semiconductor module, variations in wiring length between the semiconductor elements and emitter electrodes are small, which in turn reduces variations in load such as impedance.
As a result, it is possible to prevent overload-induced malfunction of some semiconductor elements occurring in a conventional semiconductor module, and hence, to improve the reliability of the semiconductor module.
Further, since a cross section of the wire patterns has a large size, impedance is small, and therefore, characteristics of the semiconductor module improve.
It is preferable that a surface area of said lower layer substrate is larger than a surface area of said upper layer substrate, and said connection area and said electrode pad region extend beyond said upper layer substrate covering said lower layer substrate.
With this structure, it is easy to perform wire bonding.
The first and said second semiconductor elements and said connection area may be connected with each other by bonding wires, and said electrode pad region and an external electrode may be connected with each other by a bonding wire.
The semiconductor elements may be formed by combinations of insulated gate bipolar transistors and free wheel diodes.
Further, a gel material may be injected so as to bury said lower layer substrate, said upper layer substrate, and said first and said second semiconductor elements.
This allows to fix the semiconductor elements, and hence, to improve the reliability of the semiconductor module.
As described clearly above, the wiring lengths of the semiconductor elements juxtaposed to each other are approximately uniform in the semiconductor module according to the present invention, and therefore, the reliability of the semiconductor module improves.
Also, in the semiconductor module according to the present invention, the cross section area of the wire portions increases, and therefore, impedance and the like decreases and the capabilities of the semiconductor module improve.